In the 2015 review paper 'Petawatt Class Lasers Worldwide' a comprehensive overview of the current status of highpower facilities of >200 TW was presented. This was largely based on facility specifications, with some description of their uses, for instance in fundamental ultra-high-intensity interactions, secondary source generation, and inertial confinement fusion (ICF). With the 2018 Nobel Prize in Physics being awarded to Professors Donna Strickland and Gerard Mourou for the development of the technique of chirped pulse amplification (CPA), which made these lasers possible, we celebrate by providing a comprehensive update of the current status of ultra-high-power lasers and demonstrate how the technology has developed. We are now in the era of multi-petawatt facilities coming online, with 100 PW lasers being proposed and even under construction. In addition to this there is a pull towards development of industrial and multidisciplinary applications, which demands much higher repetition rates, delivering high-average powers with higher efficiencies and the use of alternative wavelengths: mid-IR facilities. So apart from a comprehensive update of the current global status, we want to look at what technologies are to be deployed to get to these new regimes, and some of the critical issues facing their development.

/pdf/petawatt-and-exawatt-class-lasers-worldwide-10zgtun6jp.pdf

Petawatt and exawatt class lasers worldwide

We review our previous results on efficient, high-power, and compact terahertz (THz) sources based on parametric processes. By reversely stacking GaP plates, we have improved photon conversion efficiency from 25% to 40%, which corresponds to the maximum value. As the number of the plates is increased from 4 to 5, the output power is decreased due to back conversion. The corresponding peak power of the THz output reaches 4 kW. We have investigated THz generation by mixing two frequencies generated by a single Nd:YLF solid-state laser. The average output power reaches 1 μW. By introducing two Nd:YLF crystals, we significantly improved the output power to 4.5 μW. Such a configuration allows us to generate different output frequencies. We review our progress for making our THz source further compact by taking advantage of passively Q-switched laser pulses. We have demonstrated that an intracavity can be utilized to enhance the THz output powers by two orders of magnitude.

Progress in terahertz sources based on difference-frequency generation [Invited]

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

We describe a compact and efficient mid-infrared (mid-IR) source based on zinc germanium phosphide (ZGP) and cadmium silicon phosphide (CSP) optical parametric oscillators (OPOs), operating in near degenerate condition, directly pumped by a 1.94 μm thulium (Tm)-doped yttrium-aluminum-perovskite (YAP) laser. The Tm:YAP laser is passively Q-switched by a chromium-doped zinc sulfide saturable absorber, and is operated to 4 W average power with a peak power of 29 kW. The laser emission was used to pump CSP and ZGP doubly resonant linear OPO cavities, generating a maximum 3.5–4.2 μm mid-IR emission of 2.5 W for CSP and 2.3 W for ZGP, with maximum optical conversion efficiencies of 65% and 58%, respectively, achieved for the two OPO crystals.

Compact and efficient mid-IR OPO source pumped by a passively Q-switched Tm:YAP laser.

When two Nd:YLF crystals share a Cr:YAG crystal functioning as a single passive Q switch, the timing jitter between each pair of dual-frequency pulses generated by the two crystals has been reduced by a factor of 20. Such a reduction in the timing jitter allows us to generate terahertz pulses by focusing such a passively Q-switched laser beam onto a nonlinear crystal. Such a result represents the first step for us to eventually implement a compact terahertz source based on ultracompact microchip lasers.

Investigation of terahertz generation from passively Q-switched dual-frequency laser pulses.

We describe a compact, highly efficient, diode-pumped, mechanically Q-switched Tm:YAP laser operating near 2 μm. The Q-switch, based on a torsion spring resonant mirror scanner, had negligible optical loss and required very low electrical drive power. At a 10 kHz pulse repetition frequency, the laser generated an average output power of 10.5 W at 1.94 μm, Q-switched pulse energy of 1.05 mJ, a pulse length of 31 ns, and a peak power of 34 kW. The Q-switched laser exhibited maximum optical and electrical efficiencies of 51% and 26%, respectively.

High-efficiency 2 μm Tm:YAP laser with a compact mechanical Q-switch.

A miniature diode pumped Er,Yb:glass laser has been developed at the Night Vision and Electronic Sensors Directorate, U. S. Army CECOM (NVESD) for soldier applications. This device uses a single laser diode at 925 nm to end pump a 200µm x 3 mm volume of Er,Yb:glass gain media. A Co2+:MgAl2O4 passive Q-switch is used to produce 2 nanosecond pulses at a repetition rate from single shot to 20 Hertz. A nominal pulse energy of 100 microjoules is emitted, corresponds to a peak power of 50 kilowatts, which is sufficient for ranging to over 2 kilometer. The Eyesafe Microlaser was designed and demonstrated to operate over a wide temperature range without temperature control of the pump laser, a feature important for soldier applications. An desirable feature of Er,Yb:glass lasers is that they emit directly at 1.54 microns, which is important for eye safe operation and low cost fabrication.

Eyesafe erbium glass microlaser

We have explored using 808nm Vertical Cavity Surface emitting laser (VCSEL) arrays for end-pumping of Nd:YAG
lasers. A variety of laser designs were explored including a compact passively Q-switched lasers that produced a 22mJ
pulse having a pulse width of <1.5ns, and an actively Q-switched laser that produced a 40mJ pulse having a 7 ns pulse
width. The VCSEL pumped actively Q-switched laser was used as a source for sum frequency generation. Using a
2mm type II KTP and 3mm type I LBO, we generated greater than 5mJ at 355nm with a 21% THG conversion
efficiency.

Compact VCSEL pumped Q-switched Nd:YAG lasers

A diode-end-pumped Tm:YLF laser, passively Q-switched (PQS) with a Cr:ZnS saturable absorber, generated 10 mJ, 29 ns-long pulses at 1.9 μm, corresponding to a peak power of 350kW. A PQS laser operated at a maximum pulse repetition frequency (PRF) of 1 kHz, generating an average power of 10 W. The demonstrated pulse energy and average power represent significant increases over previous results with PQS Tm-doped lasers, and the 10 mJ pulse energy is comparable to that of much more complex actively Q-switched versions of such lasers. Using a cadmium silicon phosphide (CSP) optical parametric oscillator (OPO), the laser output was converted to 3.5-4.2 μm mid-IR emission. The OPO exhibited an optical efficiency of 64%, and generated 6W of mid-IR power.

Passively Q-switched 10 mJ Tm:YLF laser with efficient OPO conversion to mid-IR

We present a compact, side pumped passively Q-switched Yb:YAG laser that was operated in a burst mode with pump durations of 2-4 ms at low duty cycles. Intra-pump pulse Q-switched pulse repetition frequencies varied from 5-20 kHz depending on the transmission of the Cr:YAG saturable absorber, which was varied from 70% to 94%. Pump duration, pulse repetition frequency and output coupler reflectivity were optimized to yield maximum Yb:YAG laser average power and laser efficiency, while providing sufficient peak intensity, typically 0.3-1 MW, to enable efficient forth harmonic generation (FHG). Pulse energies and durations were in ranges of 0.3-1.8 mJ and 1.5-7ns, respectively, dependent on the unbleached transmission of the Cr:YAG saturable absorber. We achieved an optical efficiency of greater than 15% for the Yb:YAG laser. Extra-cavity 515 nm second harmonic generation (SHG) was achieved using a 5mm long KTP crystal. The 515 nm light was then frequency doubled by focusing it into a 7mm long BBO crystal, resulting in a 15% conversion efficiency from 1030nm to 257.5 nm, with an average UV power greater than 100 mW.

UV by the fourth harmonic generation of compact side-pumped Yb:YAG laser emission

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